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Work starts on Colorado's first diverging diamond highway interchange

Colorado and Grand Junction transportation officials hope drivers will take the state's first diverging diamond interchange in stride and not be thrown off by its unique design.

"At first people look at the designs, and they are thinking, 'What's going on?' " Grand Junction's engineering manager Trent Prall said. "But once you get the driver's perspective, it's pretty intuitive."

Crews began diverting traffic on Monday as they began work on the interchange at Interstate 70 and U.S. 6/50. Prall said the improved intersection should open by Dec. 15.

Grand Junction opted for the diverging diamond design over a more conventional interchange for a variety of reasons, including safety and cost, Prall said.

The diverging diamond eliminates traditional left-hand turns by crossing lanes and shifting drivers to the left side of the road. Designers say this gives drivers direct access to a left-hand ramp to get on the interstate without waiting at a traffic signal, according to the Colorado Department of Transportation.

Diverging diamond interchanges can carry much more traffic than ordinary interchanges, and the capacity for left-turn movements is double that of a conventional diamond.

There are fewer crashes at diamond interchanges, and most are less severe, according CDOT. That's mainly because the accidents that do occur are less likely to be the devastating "T-bone" variety.

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The total coast of the I-70 diamond interchange is $4 million while a more traditional interchange would have cost between $10 million and $15 million, say designers. Helping slash the cost is that there is minimal right-of-way acquisition, said Prall.

The I-70 diverging diamond is the first built in Colorado, but another one is planned for the McCaslin overpass at U.S. 36 in Louisville as part of the Phase II reconstruction of the highway, Louisville's planning director Troy Russ said.

Some 15 diverging diamonds have been built in the U.S., the first being in Springfield, Mo.

"This is a first-of-a-kind project for us, and we are very excited to implement this DDI in an area where traffic and commerce are growing rapidly," CDOT chief engineer Tim Harris said in a news release.